The present invention generally relates to a butterfly valve controlling a gas pressure and more particularly to a butterfly valve for controlling a gas pressure inside the cabin of an aircraft.
Butterfly valves are normally used for controlling the flow rate of a liquid or gaseous fluid. Conventional butterfly valves comprise to this end a closure member positioned in a valve housing for rotation about a rotation axis defined by a shaft. Typically, the closure member is configured as a disk which is rotated by the shaft between an open position allowing the fluid to flow through the valve housing and a closed position preventing the fluid from flowing through the valve housing. The shaft is driven by a torque usually applied by an external actuator, such as an electric motor.
Especially in the aviation industry, butterfly valves are employed for controlling the air pressure inside the cabin of an aircraft, as disclosed in U.S. Pat. No. 5,881,995. The flow rate of the air circulating in the cabin and, as a result, the air pressure in the cabin are influenced by the opening position of the closure member. Since air is a compressible fluid, a butterfly valve controlling the air pressure is subject to undesired effects such as vibrations, wear and noise. For example, a high pressure or a high speed flow rate of the air generates aerodynamic throttling over a wide range of opening positions resulting in an adverse state of tension in the closure member. This state of tension may effect damages of the closure member such as a crack. A spreading crack may have the consequences of breaking the closure member and, thereby, releasing a cross-sectional area of the valve housing which leads to a sudden and dangerous loss of pressure.